South Pole

The lunar south pole is situated in a huge depression, on the dark side of the Moon, leading to 16 km altitude differences over the region. The pole is of special interest to scientists because of the postulated occurrence of water ice in permanently shadowed areas around it. Of the lunar poles, the south pole is of greater interest because the area that remains in shadow is much larger than that at the north pole.[1] The lunar south pole craters are unique in that sunlight does not reach the bottom. Such craters are cold traps that contain a fossil record of the early solar system.[2]

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A peak of eternal light (PEL) is a hypothetical point on the surface of an astronomical body that is always in sunlight. Such a peak must have high altitude and be on a body with very small axial tilt. Careful analysis of imagery and topographic conditions on the lunar South Pole by teams from NASA and the ESA revealed a small number of illuminated ridges within 15 km of the pole, each of them much like an island of no more than a few hundred meters across in an ocean of eternal darkness, where a lander could receive near-permanent lighting (for ~70–90% of the southern lunar winter, and likely all of the southern lunar summer).[3]

The Malapert Mountain region, on the rim of the Malapert crater 122 km from the lunar south pole on the Earth-facing side, may also have high levels of illumination. One study estimates the Malapert Mountain region to receive less than full sunlight 11% of the time. Sunlight exposure varies by year due to the Moon's orbit being 1.5 degree off plane with the sun. 2005 estimates of sunlight coverage of the Malapert Mountain region found only six partially lit or unlit events that year: 0–159 hours of complete sunset per event and 41–199 hours of complete or partial sunset per event.[4] A later study using a combination of both Clementine imaging and SELENE topographical data estimated only 74% of full sunlight for the year 2020.[5] This study found that two points only ~8 km from each other along a straight ridge extending from Shackleton Crater at the Lunar South Pole are illuminated a combined ~94% of a lunar year. This is because both points cast shadows upon each other during different times of the lunar year, and only a few times of darkness occur when further peaks throw shadows over both of these points simultaneously.

The data set from Lunar Reconnaissance Orbiter shows that some sites on the rim of Shackelton remain illuminated for 94% of a lunar year. The longest all three Shackleton outposts are eclipsed is 43 h..[6]

MoonEx, a privately funded American company of Silicon Valley and space entrepreneurs, plans to launch Expedition: Lunar Outpost by 2020. Its purpose is to enable the first commercial presence and exploration of the lunar South Pole. MoonEx states that the poles of the Moon have concentrations of water and other valuable resources, as well as “peaks of eternal light” where nearly continuous sunshine and direct communication with Earth are possible. The primary goal for this mission is to set up the first lunar research outpost, prospect for water and useful minerals, and accommodate a variety of research instruments for the expedition partners of MoonEx.[7]